docs: def initialize(self):
          '''List all datasets for a given ...'''
          fmt = guess_format(self.source.url)
          # if format can't be guessed from the url
          # we fallback on the declared Content-Type
          if not fmt:
              response = requests.head(self.source.url)
              mime_type = response.headers.get('Content-Type', '').split(';', 1)[0]
              if not mime_type:
                  msg = 'Unable to detect format from extension or mime type'
                  raise ValueError(msg)
              fmt = guess_format(mime_type)
              if not fmt:
                  msg = 'Unsupported mime type "{0}"'.format(mime_type)
                  raise ValueError(msg)
          graph = self.parse_graph(self.source.url, fmt)
          self.job.data = {'graph': graph.serialize(format='json-ld', indent=None)}